totally agree on the fitted bodice, you live in a world with gravity.
As to the white bit, (I know this sounds crazy) try silk. Dharma Trading has it super cheap, you don't need a lot, it'll flow and float in the air like magic and it won't choke you with it's weight.
For closing the top/ shoulder thingy (I'm not sure there is a proper name for that odd collar/ cape thing), maybe I'm a bit of a purist, but I'd make the cape like part, then the collar, each as a whole item. Then I'd sew them together on one side (left) and put velcro or snaps along the top of the shoulder on the other side (right). the major over lap will hide the fact that they are separate at all.